Building a terrestrial planet requires raw materials that weren't available in the early history of the universe. The Big Bang filled space with hydrogen and helium. Chemical elements like silicon and oxygen - key components of rocks - had to be cooked up over time by stars. But how long did that take? How many of such heavy elements do you need to form planets?

Previous studies have shown that Jupiter-sized gas giants tend to form around stars containing more heavy elements than the Sun. However, new research by a team of astronomers found that planets smaller than Neptune are located around a wide variety of stars, including those with fewer heavy elements than the Sun. As a result, rocky worlds like Earth could have formed earlier than expected in the universe's history.

"This work suggests that terrestrial worlds could form at almost any time in our galaxy's history," said Smithsonian astronomer David Latham (Harvard-Smithsonian Center for Astrophysics). "You don't need many earlier generations of stars."* Latham played a lead role in the study, which was led by Lars A. Buchhave from the University of Copenhagen and will be published in the journal Nature. The work is being presented today in a press conference at the 220th meeting of the American Astronomical Society.

Astronomers call chemical elements heavier than hydrogen and helium "metals." They measure the metal content, or metallicities, of other stars using the Sun as a benchmark. Stars with more heavy elements are considered metal-rich while stars with fewer heavy elements are considered metal-poor.

Latham and his colleagues examined more than 150 stars known to have planets, based on data from NASA's Kepler spacecraft. They measured the stars' metallicities and correlated that with the sizes of the associated planets. Large planets tended to orbit stars with solar metallicities or higher. Smaller worlds, though, were found around metal-rich and metal-poor stars alike.* "Giant planets prefer metal-rich stars. Little ones don't," explained Latham.

They found that terrestrial planets form at a wide range of metallicities, including systems with only one-quarter of the Sun's metal content.

Their discovery supports the "core accretion" model of planet formation. In this model, primordial dust accumulates into mile-sized planetesimals that then coalesce into full-fledged planets. The largest, weighing 10 times Earth, can then gather surrounding hydrogen and become a gas giant.

A gas giant's core must form quickly since hydrogen in the protoplanetary disk dissipates rapidly, swept away by stellar winds in just a few million years. Higher metallicities might support the formation of large cores, explaining why we're more likely to find a gas giant orbiting a metal-rich star."This result fits with the core accretion model of planet formation in a natural way," said Latham.

The center of the magnificent barred spiral galaxy NGC 1512 at top of the page reveals a stunning 2,400 light-year-wide circle of infant star clusters. Astronomers generally believe that the giant bar, which is too faint to be seen in this image, funnels the gas to the inner ring, where massive stars are formed within numerous star clusters. NGC 1512 Located 30 million light-years away, is a neighbor of our Milky Way galaxy.

Comments

Alien Habitable Planets May Exist Billions of Years Older Than Earth --Harvard Center for Astrophysics
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And where are these civilizations Billions of Years Older Than human race? - asked Fermi billions of years ago.
The article is full of mistakes. For instance - The Big Bang filled space with hydrogen and helium. Other theories fill the space with hydrogen and helium, too.

So, okay, habitable planets could have formed billions of years ago. I've long suspected that, though I never really thought about the barriers discussed here, and the new information that makes those barriers less severe than previously thought does interest me.

My question: would these worlds still be habitable today? If we manage to achieve Alcubierre drive, wormhole generation, quantum teleportation, or some other means of (effective) FTL, could we colonize these planets? Or would their main use be to see what Earth will eventually become?

That's not really meant as argument material; I just wonder what this would be able to provide and/or teach us. (Part of my curiosity is as a sci-fi novelist; I like to try for as much scientific accuracy in my work as I can.)

Those that ask, with habitable plantets much older than ours, we should have seen alien civilizations by now, are forgetting that advanced intelligence is surely non-biological. Non-biological advanced intelligence has no interest in colonization -- they thrive more easily outside planetary gravity wells. Their primary interest will be scientific discovery and exploration, which requires being unobtrusive. We don't see them because they don't want to be seen.

We as humans seem to expect advanced intelligent life to automatically have an interest in us.

What if their culture is so different that they simply see no value in communicating with our species. What if they have a way of studying us in a way that is incomprehensible ...i.e. via telepathy, inter-dimensional shadowing.

They may view us as nothing more than primitive life forms no more advanced than a bacteria. After all, a society a million or billion years more advanced would be like unimaginable Gods to humans.

It's a bit of an assumption that a planet with life -- even complex life will eventually develop sapient life and, through it, civilization. It may or may not, and I'd say that in any individual case the odds are stacked strongly against it... and several well-learned scientists agree.

We are also assuming that intelligent life has learned to travel faster than light. There very well could be dozens of intelligent species like ours withing our own galaxy. Buuut if FTL travel is something that is infact physically impossible then we may never detect them.

Even if today we developed a super telescope that could see the terrain of distant planets it would be looking into the past. If we looked 20,000 years into our past at the earths surface we would could likely tell there is some form of vegitation but signs of intelligent life would be next to none.

Faster than light travel for an object with mass is by all known theories impossible. However, if you can create a gravitational field and then amplify it. You have now found a way to sidestep the universal speed limit and can now warp space/time so that the distances are then irrelevant. So until a species is advanced enough to create gravity or somehow learn to control it, space travel is simply limited to you're local solar system as we are.